How to Replace a Trouser Zip the Right Way

A trouser fly uses a closed-end zip

A zip in a pair of trousers is the closed-end type: the two halves are joined at the bottom by a stop, and the slider runs up and down without the zip ever coming apart in two. That is the opposite of a jacket zip, which is separating and splits completely every time you take the jacket off. The difference matters for the repair. On trousers both ends are sewn in – the top is caught under the waistband, the bottom is held by a bar tack across the tape – and the zip itself hides behind a fly with an underlap. On suit trousers it is also wrapped by lining and pocket bags. All of that has to be opened and closed again neatly if the whole zip is to be replaced.

Work out what has actually failed

Before you do anything, find out whether it is the slider or the teeth themselves – that decides whether a small knack will do or the whole zip must be replaced:

• The zip glides open by itself: you pull the slider up, but the teeth spring open again behind it. The slider is worn and no longer squeezes the teeth together – the teeth may be fine.
• Missing or bent teeth: if teeth are missing, bent or pulled off the tape, a new slider won't help – the whole zip must be replaced.
• The slider has fallen off or cracked: a single damaged slider can sometimes be replaced, but on trousers it often sits locked between the stops.
• Fabric or thread in the teeth: lining or a loose thread is wedged under the slider. That is not a broken zip but caught fabric – hold the cloth away and wiggle the slider gently free.

Sometimes it is only the slider

If the zip glides open by itself and the teeth are otherwise whole and straight, it is the slider that has given way. On a coil zip (the soft plastic type on most trousers) you can try a temporary rescue before giving up on the zip:

1. Close the zip and look: if it gapes open just behind the slider, the mouth of the slider has widened.
2. Take flat pliers and squeeze the slider gently and evenly on both sides, just a fraction, so it grips the coil more tightly again.
3. Do not use this on a metal zip – metal sliders crack easily when squeezed.
4. Test the zip a few times. If it holds, it is a reprieve, not a cure – a worn slider often loosens again.
5. To replace the slider or the whole zip for good, the waistband and fly must be opened, because the ends are sewn in – that is a sewing job.

Why replacing the whole zip in trousers is fiddly

Replacing the entire zip in a pair of trousers is more demanding than people think, and the result stands or falls on the details:

• The new zip has to match in length, tooth type (coil, metal or plastic), gauge and colour – and be a closed-end type, not a separating jacket zip.
• The top of the zip is caught under the waistband, which has to be unpicked and sewn back exactly so the waistband still meets evenly.
• The fly has a visible curved topstitch (the J-seam) at the front that must be recreated identically, or the repair looks home-made.
• On suit trousers the lining, pocket bags and an underlap sit around the zip and must be handled without pulling or twisting the fly.
• If the zip is too long, it must be shortened from the top and given new stops – not cut blindly.

Send the trousers to us

If you are unsure whether a new slider will do or the whole zip must be replaced – or you simply want the fly to look as clean as before – you can send the trousers to us. We assess the zip and replace what needs replacing, matched to tooth type, length and colour, and sew the new zip in the way it originally sat, with the same topstitch. If the trousers also need a hem or another repair, we handle it in the same round. We help you across all of Norway, you order online, and you see the price before you order.

Frequently asked questions